. >> detroit... >> chicago... >> nashville... >> los angeles... >> san francisco... >> al jazeera america, take a new look at news. tÑ the question of whether mass surveillance is effective in keeping people safe, is also at the heart of the debate over the nsa's programs. and nowhere is that debate more consequential than in washington dc's halls of power. >> it's been several months since the snowden leaks and the story isn't going away yet. now congress is holding a series of public hearings. today is the first one and we're going to hear general alexander and director clapper testify. >> what we do not do is spy unlawfully on americans or for that matter, spy indiscriminately on the citizens of any country. we only "spy" for valid intelligence purposes as authorized by law with multiple layers of oversight to ensure we do not abuse our authorities. >> nsa's programs have contributed to understanding and disrupting 54 terror-related events, 25 in europe, 11 in asia, five in africa, and 13 in the united states. this was no accident. this was not coincidence. that claim was challenged a